Support path negation with custom instructions applyTo paths

### Describe the feature or problem you'd like to solve

I want to provide broad instructions that apply to 90% of our monorepo. However they do not apply to a small subset. Rather than having to add every single path they DO apply to (hundreds), I want to be able to specify certain paths they do NOT apply to

### Proposed solution

Support negation pattern like:
```
applyTo: **/*.cpp, !/but/not/this/path/**
```

### Example prompts or workflows

I want to provide broad instructions that apply to 90% of our monorepo. However they do not apply to a small subset. Rather than having to add every single path they DO apply to (hundreds), I want to be able to specify certain paths they do NOT apply to

### Additional context

_No response_